I don't think there's a personal significance yet aside from these. In fact, in the dream, it didn't seem to be either good or bad - all I know about "Class 151" in the dream is that apparently it's a worse class and/or college than "Class 150" but a better one than "a Nazi school".

Before Pokémon Gold & Silver, there were 151 Pokémon (including Mew), but I doubt that that has anything to do with these 151s. (It is why I made a Pokémon reference in the subject line, though :P )

As for numerological significance, when I searched for 151 on Gematrix.org, I got phrases like "Jesus Christ" and "Holy Spirit" but also phrases like "Abaddon Apollyon" (though not as many), which seems to fit with 151 being neither truly good nor truly bad. Also, 151 × 6 = 906, a significant number because if you subtract 18 (6+6+6) from that, you get 888 (which represents Jesus).